1. Field of the Invention
The present invention is directed to power amplifiers, and, more particularly, to power amplifiers for high capacitive devices which require high-voltage drive and wide bandwidth.
2. Description of the Prior Art
Piezoelectric actuators and other high-capacitive devices require high voltage drive. Driving them linearly in a conventional amplifier requires a large reactive current and results in correspondingly high losses.
Piezoelectric actuators have been implemented as actuators for various wide bandwidth optical positioning and wavefront correction devices. The actuators are formed from stacks of piezoceramic wafers and appear basically as pure capacitive loads to the driving amplifier. As a consequence, almost all of the driving power is dissipated in the output stage of the amplifier. This is an advantage in thermal management of the actuators but places a heavy burden on amplifier design. The quantity of driver-dissipated, or "reactive power", is a function of the square of the driver output voltage for a given operating frequency.
Electrostatic loudspeakers are another type of high-capacitive device that requires high voltage drive and wide bandwidth. These devices contain a deformable membrane serving as one plate of a capacitor. Voltage impressed across the capacitor plates causes deformation of the membrane which couples acoustic energy into the air.
Class A, B, C amplifiers and combinations thereof are typically used to drive high-capacitive loads. Electronic vacuum tubes are capable of handling high voltage and are used in either linear or tuned amplifier applications. A linear amplifier (Class A or B) design provides wide bandwidth, but the losses are very high due to the reactive component of the load circuit. A tuned amplifier (Class C) using a tank circuit with the load capacitor forming part of the tank, will be more efficient; however, the bandwidth is not wide and depends on the quality factor, Q, of the tank circuit.